Structure-Property Relationships: Enabling a faster Commercialisation of Organic Solar Cells

The first electronic devices using organic semiconductors have just entered the market: many displays of mobile phones consist of organic light emitting diodes (OLEDs). However, these OLED-displays are considered only the first wave of organic electronic (OE) products, with organic solar cells and organic lighting expected to follow soon. Organic solar cells are currently a very active field of research, because they have the potential to become a very cheap, large area, and flexible photovoltaic technology. They furthermore can have unique properties like custom-made shapes, semi-transparency and different colours, considerably expanding the potential market to areas where current technologies are struggling. Records for conversion efficiencies have reached values above 10% and lifetimes exceeding 10 years in the laboratory, i.e. passing important milestones that are often considered as minimum requirement to become viable for commercial applications.
However, one major challenge for industry trying to commercialise this technology is: for any kind of device using thin organic semiconducting layers, its electrical and optical properties strongly depend on molecular arrangement in the organic layer, in particular for organic solar cells. To a large extent, the interdependencies between molecular structure, processing, morphology in the thin organic film, and the device properties is a black box. The current approach for improving solar cells is to make more new molecules and to run an extensive process optimisation and device testing, but there are nearly unlimited options of organic chemistry and many degrees of freedom in process parameters. This nearly trial-and-error process is consuming time and money, as well as carrying the risk that the best organic semiconductors are discarded due to wrong processing. Our project will look into this black box in a close collaboration of four industrial partners (Merck Chemicals Ltd, Kurt J. Lesker Company Ltd, Eight19 Ltd, Oxford PV Ltd) and three academic partners (ISIS Neutron and Muon Source, Diamond Lightsource, University of Oxford) and subsequently develop ways to optimise the manufacturing of organic solar cells. This involves optimisation along the complete value chain, from the design and synthesis of organic semiconductors, the development of manufacturing equipment, to the final production of organic solar cells. If successful, this project will lead to a faster market introduction of thin film solar cells that have the potential to transform the way we use solar energy.

There will be important social, environmental and economic benefits to the UK through this project. Organic solar cells have the potential to significantly contribute to the clean energy supply. Their flexibility - both in terms of mechanics and design - allow the excellent integration in places so far little used for solar energy conversions, e.g. building facades, considerably expanding the area usable for photovoltaics. Additionally, organic solar cells don't rely on scarce elements and can in principle be scaled to terawatt in installed capacity. The reduction of CO2 emissions by 80% by 2050 compared to 1990 is a central goal of the UK government. This will require a significant share from renewable sources. Organic solar cells have the potential to significantly contribute to this goal. This will also reduce the UK's dependence on energy imports and additionally stabilize energy prices. The latter will lead to a reduction of the associated risk to many UK companies and reduce the likelihood for households to end up in energy poverty. Last but not least using such solar cells will reduce CO2 emissions globally and thus help to stabilise the climate and reduce the likelihood of severe weather events.
Helping chemical companies to design better materials for organic solar cells, tool manufacturers to develop suitable coating equipment and processes, and establishing a manufacturing base for cheap solar cells in the UK will create jobs in the green sector for many years to come. Given the targeted market size of several terawatt of installed capacity of solar cells, there are plenty of opportunities for chemical companies like Merck and tool manufacturers like Lesker to grow their business, and enough room even for competing SMEs like Eight19 and Oxford Photovoltaics to get to a healthy market share.
Furthermore, organic solar cells are only one part of the much larger field of organic electronics that faces similar challenges in understanding structure-property relationships. According to market forecasts, the market for organic electronics is expected to grow by more than 30% annually and should reach a volume of more than USD 40billion in 2018 (Transparency Market Research, 2012). The developed guidelines on material design, tools and process optimisation will help all industry catering the field of organic electronics to better exploit this market. Organic electronics has already lead to fixed displays from organic light emitting diodes (OLEDs) for mobile phones. This technology is expected to become the dominant display technology for mobile phones this year. Large TVs made from OLEDs have just entered the market, as well as curved OLED displays as predecessor to truly flexible OLED displays. Many more applications of organic electronics are at various stages of research, and some may not yet have been thought, yet can have a profound impact on many people.